1. Field of the Invention
The present invention relates to a thermal sensing structure for sensing temperature of, for example, a battery of an electric vehicle, and relates to an insulating structure of a thermal sensing circuit for sensing temperature of, for example, a battery of an electric vehicle.
2. Description of the Related Art
FIG. 6 shows an embodiment of a conventional thermal sensing structure (See Patent Document 1).
In this structure, a circuit board 42 is arranged in an insulating synthetic resin made case 41. A thermal sensor 43 such as a thermistor is connected to the circuit board 42. The thermal sensor 43 is received in a recess 44 at an inside of the case 41. The recess 44 is filled with resin material 45. The thermal sensor 43 is brought into contact with a battery 47 via the resin material 45 and an upper wall 46 of the case 41 to sense the temperature of the battery 47. In this embodiment, the battery 47 is set in the case 41 for charge.
FIG. 7 shows another embodiment of the conventional thermal sensing structure (See Patent Document 2).
In this structure, a thermal sensor 52 is connected to two lead wires 51. Each lead wire 51 is covered with a protective tube 53. The thermal sensor 52 and connecting parts 54 of the lead wires 51 are covered with an insulating resin 55 such as an epoxy resin. The insulating resin 55 is sandwiched by the batteries 56 at the left and right sides. The thermal sensor 52 senses the temperature of the batteries 56.
In Patent Document 2, a flat circuit structure (not shown) in which two lead wires are covered by two front and rear insulating sheets (films), and a thermal sensor connected to the lead wires is interposed between the two insulating sheets is described.
Further, in Patent Document 3, it is described that a PTC device is connected between two metallic lead boards, and an outside of the PTC device is protected by covering it with an insulating resin (not shown). PTC is an abbreviation of “POSITIVE TEMPERATURE COEFFICIENT”. The PTC device is normally a several dozen milliohm resistor. However, owing to an abnormal energization or temperature rise, the PTC device becomes several dozen ohm resistor in a short time, and returns to an original resistor when an outside environment returns to a normal condition. The PTC device is used as a thermal sensor.
FIG. 14 shows an embodiment of a conventional insulating structure of a thermal sensing circuit (See Patent Document 2).
In this structure, a thermal sensor 132 such as a thermistor is connected to tip ends of two metallic lead wires 131 with solder. Two insulating films 133 sandwich the lead wires 131 and the thermal sensor 132 to isolate them from an outside. The thermal sensing circuit 134 is composed of the lead wires 131, the thermal sensor 132, and the insulating films 133.
As the temperature increases, the resistivity of the thermistor decreases. When a plurality of thermal sensors are arranged in the thermal sensing circuit 134, two wide insulating films sandwich pairs of lead wires 131 and the thermal sensors 132 connected to respective pairs of lead wires 131. It is widely known that the PTC device can be used instead of the thermistor.
FIG. 15 shows an embodiment of an insulating structure of the PTC device (See Patent Document 3).
In this structure, the PTC device 143 is connected to two metallic lead plates 141 via thin metallic plates 142. The PTC device is covered with insulating resin 144. As the temperature increases, the resistivity of the PCT device 143 increases. The PTC device 143 in this embodiment is not used as a thermal sensor, but a fail-safe device in which the lead plates 141 are connected to respective batteries of a high voltage battery for the electric vehicle.
[Patent Document 1] Japanese Published Patent Application No. 2001-185239 (FIGS. 1 to 3)
[Patent Document 2] Japanese Published Patent Application No. H08-128901 (FIGS. 1 and 7)
[Patent Document 3] Japanese Published Patent Application No. H07-57721 (FIG. 1)
However, in the conventional thermal sensing structure, when a hard circuit board 42 is used, the structure becomes large and expensive. Further, when using the lead wires 51 (including a case that the lead wires are interposed between two insulating sheet), it is hard to connect a plurality of thermal sensors 52, and if possible, many man-hours are needed, and the structure becomes expensive. Further, flexibility is reduced due to two insulating sheets so that the thermal sensor interposed between the insulating sheets may not be in press-contact with a battery. Further, by bending the insulating sheets forcedly, the insulating sheets and the lead wires (circuit) may receive great stress.
Further, in the conventional insulating structure of the thermal sensing circuit shown in FIG. 14, because the lead wires 131 and the thermal sensor 132 are sandwiched by two insulating films 133, the flexibility of the circuit 134 is reduced, and it may be hard to arrange the circuit along a curved surface of the high voltage battery, and to arrange the circuit along each battery disposed in a step shape.
Further, when a plurality of thermal sensors 132 is connected in series to two lead wires 131, soldering operation to connect the thermal sensor 132 to the lead wires 131 separated from the insulating films 133 may be difficult. Further, because wide insulating films 133 are used, the insulating structure becomes expensive.
Accordingly, an object of the present invention is to provide a thermal sensing structure which is compact, allowed to be assembled to a battery (an object to be sensed) side, allowed to arrange a plurality of thermal sensors at low cost, and allows a thermal sensor to be surely in press-contact with a battery (an object to be sensed) without providing great stress to insulating sheets and a circuit.
Another object of the present invention is to provide an insulating structure of a thermal sensing circuit having good flexibility to be easily adapted to an arrangement or a shape of an object to be sensed, being at low cost, and able to improve insulating reliability of a thermal sensing part.